Process of etching beryllium



United States Patent 3,488,238 PROCESS OF ETCHING BERYLLIUM Walter Batiuk, Seattle, and Terry A. Hallberg, Edmonds, Wash., assignors to The Boeing Company, Seattle, Wash., a corporation of Delaware No Drawing. Filed Jan. 14, 1966, Ser. No. 520,650 Int. Cl. C23f ]/00, 17/00 US. Cl. 156-18 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the surface treatment of electrical conductor materials from the group consisting of group II alkaline earth metals (specifically, beryllium, magnesium, calcium, strontium, barium, and radium), and, more specifically, to a process for the etching of the metal beryllium and to a chemical solution composition for such etching.

During manufacture of beryllium components involving, for example, hot forming operations, oxide coatings are formed on the surfaces of the beryllium articles. This particular oxide of beryllium is very tenacious and varies unevenly in thickness. Since beryllium is a good conductor of electricity, the presence of such an oxide would limit the usefulness of any electrical component which consists in part of beryllium.

Commonly, chemical systems are used for de-scaling (deoxidizing) and etching beryllium. These systems have proven slow in removing the oxide and have resulted in uneven etching of the beryllium. The commonly used chemical systems also require two separate solutions: one for deoxidizing, the other for etching. An example of such a common method of etching is set forth in the Patent No. 3,083,451 to Atkinson. The subject patent deals with beryllium brazing and sets forth that before brazing, the beryllium can be etched, using a 5% solution of hydrofluoric acid in alcohol. As will be seen below, the method and chemical composition of the instant invention provides a definite improvement over such commonly used etchant solutions and commonly used processes. Another method commonly used to deoxidize and etch beryllium combines the deoxidation of the beryllium in nitric hydrofluoric acid solution, followed by a 'water rinse and then an etching of the part in sulfuric-chromic-phosphoric acid solution. This method is inadequate because of the slow oxide removal and the preferential (uneven) etching action of the method, which therefore is both undesirable and ineflicient.

In carrying out the instant invention, one feature eliminates the adverse effects illustrated in commonly used methods through the use of an ammonium bifluoridephosphoric acid solution. When used, this solution deoxidizes and ctches the beryllium faster. The solution also produces an evenly etched, superior surface (a most important factor) than separate solutions previously used.

Another feature of the instant invention proves this process to be both efficient and economical, for it requires only: (1) a room temperature operating condition and (2) a one solution dip to effectively deoxidize and etch beryllium.

It is therefore an object of the present invention to provide an improved etch for the surfaces of electrical conductor materials taken from the group II alkaline earth metals.

It is a further object of the present invention to provide an improved etch for the surfaces of beryllium articles.

It is a still further object of the present invention to pro vide an improved etch to remove oxides from the surface of electrical conductor metals from the group II alkaline earth metals.

It is a still further object of the present invention to provide an improved etch for the exposed surfaces of a beryllium article whereby the oxidation and etching is accomplished by a single solution.

The novel features characteristic of the instant invention, including its organization and method of operation, as well as further objects and advantages thereof can be better understood from the following description in which a presently preferred embodiment of the invention is presented by way of example. It should be understood, however, that the description is for the purpose of illustration only and that the true spirit and scope of the invention is defined by the accompanying claims.

Briefly, the improved etch of the present invention comprises approximately 10% (by weight) ammonium bifluoride and 10% (by weight) of 85% phosphoric acid in water; however, other varying compositions of the constituents have been found effective. Briefly in operation, the deoxidizing step comprises immersing a cleaned part of beryllium in ammonium bifluoride-phosphoric acid solution at approximately to 100 F. for approximately three minutes (temperature is not critical). The etching process takes place after removal of the oxide during the above immersion step. The beryllium part is re-immersed at approximately one minute intervals until the desired thickness reduction is obtained. The rate of etching is approximately mil per minute per side of part at approximately 100 F. However, this rate is adjustable by raising and/ or lowering the temperature and/ or solution concentration.

A presently preferred solution and procedure of the present invention is outlined below and is recommended for deoxidizing, etching and desmutting of beryllium parts. The recommended solutions set forth below have faster etching rates and produce an evenly etched surface as compared to the slow etching and preferential (i.e., uneven) etching action of the previously used solutions. The preferred solution can be conveniently prepared by filling a container with approximately 75 gallons of water; pounds of ammonium bifluoride, purified flake, is then added and mixed until completely dissolved; next, ten gallons of 85% phosphoric acid is added and mixed; finally, the container is filled to the IOO-gallon mark with water and the entire solution is thoroughly mixed. In this preferred embodiment of the deoxidizing and etching solution, the relative proportions of ingredients are as follows:

Moles Ammonium bifluoride 2.2-2.99 Phosphoric acid 0.670.84

The solution should be maintained at a temperature of approximately 70 to 100 F. The recommended temperature for rapid metal removal is to F. The preceding solution will rapidly remove surface oxides from group II alkaline earth metals and in particular beryllium metals, an etching time of approximately 20 seconds being sufiicient to remove the oxide coatings commonly formed during the fabrication of diffused beryllium parts. In applications where etching times are not critical, the relative proportions of the ingredients can be varied over a much wider range. Since the etching effectiveness of hydrofluoric acid solutions are well known, one skilled in the art is able to estimate permissible dilutions for a specific application.

The next step in the procedure requires the removal of any smutting of the beryllium parts due to the action of the ammonium bifiuoride-phosphoric acid solution. The preferred embodiment of the desmutting solution is a sulfuric-chromic-phosphoric acid solution. For each 100 gallons of final solution the preferred embodiment is made as follows: pour 4 /2 gallons of tap water into a tank; add 93 pounds of technical grade chromium trioxide and mix thoroughly until the solution becomes saturated with the trioxide; add 87 /2 gallons of 85% phosphoric acid and mix; add four gallons of sulfuric acid and mix thoroughly. In this preferred embodiment the relative proportions of the ingregients are as follows: sulfuric acid, 0.61 to 0.84 moles; chromic acid (CrO 1.12 to 1.27 moles; phosphoric acid (H PO 12.2 to 13.4 moles; and water 1.66 to 3.32 moles. The controlled temperature for the above solution is 70 to 110 F.

The following procedure is the preferred sequence for performing the etching and desmutting method using the above preferred solutions. The beryllium part is immersed in the ammonium bifiuoride-phosphoric acid solution at 70 to 100 F. for approximately three minutes. The oxide removal rate is dependent upon the temperature of the solution and upon the type of oxide present on the base metal. If oxide removal is complete within one to two minutes, except for some heavy oxide areas, a fine emery cloth (wet) is used to remove the oxide in these stubborn areas. Precaution should be taken to confine the dust particles produced by the emery sanding to the deoxidizing solution in the tank. Because of the various types and thicknesses of oxide present on the parts, it is best to remove the parts every minute for observation and milking. Once the oxide is removed, the solution etches the base metal at the approximate rate of mil per minute per side at 90 to 100 F. Upon removal of all the oxide, the part is re-immersed in the ammonium bifiuoride-phosphoric acid solution (in approximately three one-minute intervals) until the part thickness is reduced by two to three mils per side of part. The purpose of the two to three mils per side removal requirement is to remove the stress risers formed on the surface during the heat treat and forming. Beryllium is an extremely hard metal and stress risers are predominant. Failure to remove the stress risers will cause the part to crack upon further working. When the ammonium bifluoride-phosphoric acid solution exceeds 100 F., remove the parts until the solution has cooled down to the allowable solution temperature. Next, the parts are rinsed in tap water.

To desmut, the process is as follows: the beryllium part is immersed in the sulfuric-chromic-phosphoric acid solution at 70 to 110 F. for approximately one to three minutes, dependent upon the solution temperature and upon the degree of polishing desired. Although this sol-ution is meant to remove the smut formed during the etching phase, this solution will also polish the surface. Usually a minimum amount of polishing is desired for brazing purposes. The longer the exposure of the part to the desmutting solution, the brighter the part will appear; however, the surface will increase in roughness if the desmutting solution is allowed to contact the part for too long a time. Next, the part is rinsed in tap water until all signs of the desmutting solution on the parts has been completely removed. The part is air dried and wrapped in clear polyethylene or polyvinyl film before shipping.

Thus, there has been described an improved etchant solution and etchant process for the removal of oxides from the surfaces of group II alkaline earth metals without surface staining and very little undercutting of an applied etchant mask.

Although the invention has been described with a certain degree of particularity, various modifications of the proportions of the specified ingredients may occur to those skilled in the art when considering certain specific applications of the etchant. Such-modifications are considered within the spirit and scope of the present invention as defined by the following claims.

We claim:

1. In a process for removing oxides from an article having a surface consisting of a beryllium metal and noncomitant etching of the article surface, an aqueous solution comprising:

(a) 2.2 to 2.99 moles of ammonium bifiuoride; and

(b) 0.67 to 0.84 moles of phosphoric acid.

2. The process of removing oxides from a beryllium metal surface and etching the surface comprising the steps of:

(a) applying to the surface an aqueous solution which comprises 2.2 to 2.99 moles of ammonium bifiuoride and 0.67 to 0.84 moles of phosphoric acid; and

(b) desmutting the surface by applying thereto a solution comprising 0.61 to 0.84 moles of sulfuric acid, 1.12 to 1.27 moles of chromic acid, 12.2 to 13.4 moles of phosphoric acid, and 1.66 to 3.32 moles of water.

3. The process of removing oxides from a beryllium metal surface and of concomitantly etching said surface comprising the step of applying to the oxides and to the metal surface an aqueous solution which comprises 2.2 to 2.99 moles of ammonium bifiuoride and 0.67 to 0.84 moles of phosphoric acid.

4. The process of removing oxides from the surface of a beryllium metal and etching said surface comprising the step of immersing the metal in an aqueous solution which comprises 22 to 2.99 moles of ammonium bifiuoride and 0.67 to 0.84 moles of phosphoric acid.

5. The process as claimed in claim 4 whereinsaid aqueous solution is maintained at a temperature of about F. to F.

References Cited UNITED STATES PATENTS 3,107,188 10/1963 Hancock 15617 OTHER REFERENCES Chemical Milling of Beryllium. Missel et al., Metal Finishing, November 1965, Vol. 63, No. 11, pp. 69-71.

JACOB H. STEINBERG, Primary Examiner US. or. X.R. 252-792, 79.3 

